yes u may drop off ur old 40gb hdd into the new system for copying but remember to slave the 40gb before u start it up, (unless its a Sata)
Dont worry it wont damage ur new system
about ur PSU make sure it actually came from ur PSU before u start buying thing that are not needed. check ur power connector to the mobo, try opening up ur PSU to see any burnt marks, etc...
BTW u double posted!i!i!i